Light-induced plating

ABSTRACT

An apparatus for the light-supported precipitation of an electrolyte on a semiconductor component comprises a plating bath with an electrolyte, a first electrode arranged in the plating bath and a second electrode arranged outside the plating bath, a holding device for the semiconductor component and an irradiation device for irradiating the semiconductor component with electromagnetic radiation, the irradiation device being arranged outside the plating bath.

FIELD OF THE INVENTION

The invention relates to an apparatus and a method for thelight-supported precipitation of a metal from an electrolyte on asemiconductor component. The invention also relates to a semiconductorcomponent.

BACKGROUND OF THE INVENTION

Light-induced and light-supported galvanic processes are suitable forthe production of highly efficient solar cells. Generally, the lightsource for such methods is located opposite the front side of the solarcell, the electrolyte being arranged between the solar cell and thelight source. What is disadvantageous here is that the electrolyteabsorbs more or less of the light of the light source. Moreover, a lightsource arranged directly in front of the surface to be coated adverselyaffects, on the one hand, convection directly in front of the electrodeand, on the other hand, stream line distribution, which can have a veryadverse effect on the galvanic process. Finally, if the light source isarranged in the galvanic bath, the constructional and safety effort isconsiderable.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of improving an apparatusand a method for the light-supported precipitation of a metal from anelectrolyte on a semiconductor component. The invention is also based onthe object of creating an improved semiconductor component.

Said objects are achieved by an apparatus for the light-supportedprecipitation of a metal from an electrolyte on a semiconductorcomponent comprising a plating bath with an electrolyte, a firstelectrode arranged in the plating bath and a second electrode arrangedoutside the plating bath, a holding device for the semiconductorcomponent and an irradiation device for irradiating the semiconductorcomponent with electromagnetic radiation, the irradiation device beingarranged outside the plating bath and the electrolyte forming a layerwith a layer thickness of a maximum 10 mm between the semiconductorcomponent and the irradiation device. Furthermore, said objects areachieved by a method for producing a semiconductor component comprisingthe steps of providing a plating bath with an electrolyte, a firstelectrode arranged in the plating bath and a second electrode arrangedoutside the plating bath, providing an irradiation device for generatingelectromagnetic radiation, providing a semiconductor substrate of aplanar design with a first side and a second side lying oppositethereto, immersing at least the second side of the semiconductorsubstrate into the electrolyte, producing an electrical contact betweenthe first side of the semiconductor substrate and the second electrode,and irradiating at least the first side of the semiconductor substrateby means of the irradiation device. Said objects are further achieved bya method according to the invention, wherein the first side of thesemiconductor substrate is its front side. The core of the inventionconsists in arranging the irradiation device for the irradiation of thesemiconductor component outside the plating bath.

The irradiation device is preferably arranged on the semiconductorcomponent side not to be coated, i.e. the semiconductor component isilluminated from the side not to be coated.

As a light source there is advantageously considered an arrangement oflight-emitting diodes and/or one or a plurality of halogen lamps. Theelectromagnetic radiation generated by the irradiation device preferablyexhibits an intensity maximum in the red to near-infrared range.

The method according to the invention is characterised in that thesemiconductor substrate is immersed into the electrolyte with at leastone first side, while it is irradiated by the irradiation device on thesecond side lying opposite to the first side.

The semiconductor substrate is preferably immersed into the electrolyteonly so far that the second side remains dry.

Alternatively, full immersion of the semiconductor substrate in theelectrolyte is possible such that the second side is covered with only afew milli-metres of electrolyte.

Features and details of the invention result from the description ofseveral embodiments based on the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a schematic representation of the apparatus for thelight-supported precipitation of an electrolyte on a semiconductorcomponent according to a first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a first embodiment of the invention is described withreference to FIG. 1. An apparatus for the light-supported precipitationof an electrolyte on a semiconductor component 1 comprises a platingbath 2 with an electrolyte 3, a first electrode 4 arranged in theplating bath 2 and a second electrode 5 arranged outside the platingbath 2. The electrolyte 3 contains at least some cobalt and/or nickeland/or silver and/or copper and/or tin and/or a compound of said metals.The electrodes 4, 5 are electrically conductively connected to a voltagesource 14. Instead of the voltage source 14 there can also be envisagedonly an electrical contact with the electrically conductive connectionof the electrodes 4 and 5.

The semiconductor component 1 is especially a solar cell. Thesemiconductor component 1 comprises a semiconductor substrate 6 of aplanar design with a first side 7, a second side 8 lying oppositethereto and a thickness D in a direction vertically to the sides 7, 8.According to the first embodiment, the first side 7 of the semiconductorsubstrate 6 is its rear side. The semiconductor substrate 6 consists atleast partly of silicon. Other semiconductor materials are, however,also conceivable.

The apparatus also comprises a holding device 9 for holding thesemiconductor component 1. The holding device 9 comprises at leastthree, especially a plurality of supports 10, by means of which theposition of the semiconductor component 1 is fixable in the apparatus.The supports 10 are arranged in the plating bath 2. They are especiallyattached to a floor 11 of the plating bath 2. The supports 10 arepreferably adjustable sideways, i.e. in the direction parallel to thefloor 11 and thus parallel to the sides 7, 8 of the semiconductorsubstrate 6. This way it is possible to ensure that they are positioned,with respect to the semiconductor component 1, at predeterminablepoints, e.g. in the area of a busbar and/or lying opposite thereto.Advantageously, the supports 10 are designed to be height-adjustable.For height adjustment, there is preferably envisaged an adjustmentdevice 12 indicated only schematically in FIG. 1.

Furthermore, the apparatus comprises contact elements 13 forelectrically contacting the semiconductor component 1. The contactelements 13 are preferably designed as spring load mounted contact pins.They are electrically conductively connected to the second electrode 5.They are also electrically conductively connectable to the first side 7of the semiconductor substrate 6. The contact elements 13 can bedesigned to be part of the holding device 9. Advantageously, the contactelements 13 are each arranged in extension of one of the supports 10.Hence, they each stand opposite one of the supports 10 with respect tothe semiconductor substrate 6. This prevents bending of thesemiconductor substrate 6. The contact elements 13, especially theirelectrical connection to the second electrode 5, are preferably arrangedoutside the plating bath 2.

Finally, the apparatus comprises an irradiation device 15 forirradiating the semiconductor component 1 with electromagneticradiation. The irradiation device 15 is advantageously arranged outsidethe plating bath 2. It is thus arranged on the side 7 of thesemiconductor component 1 facing away from the side 8 to be immersedinto the plating bath 2. The irradiation device 15 comprises at leastone light source 16 designed as a light-emitting diode (LED). The lightsource 16 comprises especially a plurality of LEDs. The LEDs arearranged in a raster of planar design.

The electromagnetic radiation generatable by means of the irradiationdevice 15 exhibits at least a portion, especially an intensity maximum,in the wavelength range of 650 nm to 1200 nm, especially in the range of840 nm to 1050 nm, especially in the range of 940 nm to 970 nm. It isthus electromagnetic radiation with a portion in the red tonear-infrared range. The output radiatable by the irradiation device 15is at least 100 mW, especially at least 1 W. The irradiation device 15is controllable by means of a control device 18 illustrated onlyschematically in FIG. 1.

According to the first embodiment, the first side 7 of the semiconductorsubstrate 6 is its rear side. Decisive for the method according to theinvention is that the first side 7 facing the irradiation device 15 isdesigned such that it is, at least in some areas, at least partly,especially at least 50% permeable for the electromagnetic radiation fromthe irradiation device 15.

The semiconductor substrate 6 is thus designed such that it is at least50% permeable, at least in some areas, in at least one direction forelectromagnetic radiation from the irradiation device 15 up to apenetration depth of at least 50%, especially at least 75%, especiallyat least 90% of the thickness D.

To this end it exhibits a metalisation 19 on the first side 7 of thesemiconductor substrate 6, which is designed to be at least partlytransparent. The metalisation 19 is preferably designed as a grid.Alternatively, the metalisation 19 can also be designed as a transparentsemiconductor or as a metal layer that is only a few nanometres thin andthus transparent. Finally, the semiconductor component 1 can alsoexhibit on the first side 7 of the semiconductor substrate 6 ametalisation of planar design with laser-fired contacts, at which themetalisation 19 is selectively opened and thus permeable for theelectromagnetic radiation generated by the irradiation device 15.

The second side 8 of the semiconductor substrate 6, which side is to beimmersed into the electrolyte 3 and faces away from the irradiationdevice 15, exhibits predetermined precipitation areas 20, on which thegalvanic precipitation of the electrolyte 3 occurs. The precipitationareas 20 are preferably designed as a seed layer applied onto thesemiconductor substrate 6 by means of fine line printing. Alternatively,the precipitation areas 20 may be designed as apertures in ananti-reflection layer on the second side 8 of the semiconductorsubstrate 6.

The following describes the function of the apparatus on the basis of amethod, according to the present invention, for producing asemiconductor component 1. According to the method according to thepresent invention, there is first provided the plating bath 2 with theelectrolyte 3 and the electrodes 4, 5 as well as the irradiation device15. Next, the semiconductor substrate 6 is arranged in the holdingdevice 9 with the second side 8 of the semiconductor substrate 6 facingthe electrolyte 3. Then, the semiconductor substrate 6 is immersed, withits second side 8, into the electrolyte 3 by adjusting the supports 10by means of the adjustment device 12. The semiconductor substrate 6 ispreferably immersed into the electrolyte 3 only in part, especially onlyso far that the first side 7 remains dry. To this end, the semiconductorsubstrate 6, after immersion in the electrolyte 3, is lifted back out ofthe electrolyte 3 by pushing out the supports 10 so far that a surfacemeniscus 17 forms between the second side 8 of the semiconductorsubstrate 6 and the electrolyte 3. The second side 8 is thus at leastlargely, especially fully in direct contact with the electrolyte 3. Thefirst side 7 of the semiconductor substrate 6, however, is above theelectrolyte 3 in the plating bath 2.

Alternatively, the semiconductor substrate 6 is immersed fully into theelectrolyte 3, however, only so far that the first side 7 is covered bythe electrolyte 3 by a layer with a depth of a maximum 10 mm, especiallya maximum 5 mm, especially a maximum 2 mm. The electrolyte 3 thus formsbetween the semiconductor component 1 and the irradiation device 15 alayer with a layer thickness of a maximum 10 mm, especially a maximum 5mm, especially a maximum 2 mm. The layer thickness is preferably 0 mm,i.e. there is no electrolyte 3 between the semiconductor component 1 andthe irradiation device 15.

The first side 7 of the semiconductor substrate 6 is electricallyconductively connected to the second electrode 5 arranged outside theplating bath 2. For the light-induced or light-supported galvanicprecipitation of a metal from the electrolyte 3 on the second side 8,the first side 7 of the semiconductor substrate 6, which side 7 liesopposite the second side 8 to be coated, is irradiated by means of theirradiation device 15. Owing to the appropriately selected spectralrange of the irradiation device 15, especially in the red tonear-infrared range, the electromagnetic radiation generated by means ofthe irradiation device 15 exhibits a depth penetration into thesemiconductor substrate 6 of at least 100 μm, especially at least 150μm, especially at least 180 μm. Thus, free charge carriers are generatedin the semiconductor substrate 6 near the PN junction of thesemiconductor substrate 6 by the electromagnetic radiation produced bymeans of the irradiation device 15. Said free charge carriers lead to acurrent flow in the circuit formed by the electrodes 4, 5 and thesemiconductor component 1 and thus to a galvanic precipitation of theelectrolyte 3 in predeterminable areas on the second side 8 of thesemiconductor substrate 6.

In a second embodiment the irradiation device 15 comprises, instead ofthe LEDs, at least one halogen lamp as a light source 16. Said lamp hasa broad spectrum with a large portion in the long-wave range. This wayit is ensured that a sufficient portion of the electromagnetic radiationemitted by the irradiation device 15 exhibits a penetration depth of atleast 50%, especially at least 75%, especially at least 90% of thethickness D of the semiconductor substrate 6, and that in this way thefree charge carriers produced by the irradiation device 15 in thesemiconductor substrate 6 reach the PN junction of the semiconductorsubstrate 6.

According to a third embodiment of the invention, the second side 8 ofthe semiconductor substrate 6 is the rear side of a solar cell. Thefirst side 7 thus forms the light incidence side of the solar cell. Onthis embodiment, the second side 8 is preferably designed as an openedanti-reflection layer, but it may also be coated across its entiresurface. On this embodiment, the contact elements 13 are preferablyarranged on the conductor paths formed by the metalisation 19 designedas a grid and/or the busbars of the semiconductor component 1.

According to a fourth embodiment of the invention, the supports 10 serveto produce an electrical contact between the second side 8 and thesecond electrode 5. To this end, the supports 10 are electricallyconductively connected to the second electrode 5. They are designed tobe insulated from the electrolyte 3. This embodiment is particularlysuited for galvanic thickening of the contacts on the rear side of anemitter-wrap-through solar cell.

According to a fifth embodiment of the invention, the galvanic bath 2 isdesigned as a so-called cup plater for the application of fountainplating. Such a cup plater is e.g. known from DE 10 2007 020 449 A1.Here, the plating bath 2 comprises a preferably hollow cylinder-shapedinsert, which, in the area of the floor 11, exhibits an aperture fromwhich electrolyte 3 continuously flows into its interior space. To thisend, the electrolyte 3 is pumped through the aperture on the floor 11into the interior space of the insert by means of a pump. Theelectrolyte 3 pumped into the interior space flows over an upper rim ofsaid insert. The insert protrudes clearly from the surface of theelectrolyte 3 in the plating bath 2. The insert has, especially in thearea of its upper rim, a cross-section that is adapted to the size andshape of the semiconductor substrate 6. During operation of theapparatus, the semiconductor substrate 6 is arranged such on the rim ofthe insert, which serves as supports 10, that the second side 8 facesthe interior space of the insert. The electrolyte 3 flowing through theaperture into interior space of the insert thus flows past the secondside 8 of the semiconductor substrate 6. As a result of the continuousflow of the electrolyte 3 generated by the pump, there is ensured on theone hand good convection in the immediate electrode vicinity, and on theother hand the semiconductor substrate 6 is pushed against the rimserving as supports 10 and is, as a result, fixed to preventdisplacement. With this arrangement, especially the first side 7 ofsemiconductor substrate 6 is kept dry.

The apparatus can, of course, also be designed as an in-line plant, withthe semiconductor component 1 being transportable parallel to the sides7, 8 of the semiconductor substrate 6 through the apparatus by means ofa transportation device not shown in FIG. 1, and the supports 10 beingdesigned as rollers on which the semiconductor substrate 6 is movablethrough the plant, and especially the contact elements 13 also beingdesigned as rollers.

In a vertical design the semiconductor substrate 6 is attached to asteel strap, by which it is at the same time contacted and guidedvertically through the plating bath 2. During this, the semiconductorsubstrate 6 side 7, 8 to be irradiated is guided as closely as possiblepast a transparently designed wall of the plating bath 2, on the rearside of which, i.e. opposite, relative to the wall, of the side 7, 8 tobe irradiated, the irradiation device 15 is arranged. The side 7, 8 tobe irradiated is preferably the rear side of the semiconductor component1.

1. An apparatus for the light-supported precipitation of a metal from anelectrolyte on a semiconductor component (1) comprising a. a platingbath (2) with i. an electrolyte (3), ii. a first electrode (4) arrangedin the plating bath (2) and iii. a second electrode (5) arranged outsidethe plating bath (2), b. a holding device (9) for the semiconductorcomponent (1) and c. an irradiation device (15) for irradiating thesemiconductor component (1) with electromagnetic radiation, d. theirradiation device (15) being arranged outside the plating bath (2) ande. the electrolyte forming a layer with a layer thickness of a maximumof 10 mm between the semiconductor component (1) and the irradiationdevice (15).
 2. An apparatus according to claim 1, wherein theirradiation device (15) comprises at least one light-emitting diode(LED).
 3. An apparatus according to claim 1, wherein the irradiationdevice (15) comprises a plurality of LEDs.
 4. An apparatus according toclaim 1, wherein the irradiation device (15) comprises at least onehalogen lamp.
 5. An apparatus according to claim 1, wherein theelectromagnetic radiation generatable by means of the irradiation deviceexhibits at least a portion in the red to near-infrared wavelengthrange.
 6. An apparatus according to claim 1, wherein the portion in thered to near-infrared wavelength range, exhibited by the electromagneticradiation generatable by means of the irradiation device, is anintensity maximum.
 7. An apparatus according to claim 1, wherein theelectromagnetic radiation generatable by means of the irradiation deviceexhibits at least an intensity maximum in the read to near-infraredwavelength range in the range of 650 nm to 1200 nm.
 8. An apparatusaccording to claim 1, wherein the electromagnetic radiation generatableby means of the irradiation device exhibits at least an intensitymaximum in the read to near-infrared wavelength range in the range of840 nm to 1050 nm.
 9. An apparatus according to claim 1, wherein theelectromagnetic radiation generatable by means of the irradiation deviceexhibits at least an intensity maximum in the read to near-infraredwavelength range in the range of 940 nm to 970 nm.
 10. An apparatusaccording to claim 1, wherein the holding device (9) comprises at leastthree supports (10) which are arranged in the plating bath (2).
 11. Anapparatus according to claim 1, wherein the holding device (9) comprisesa plurality of supports (10) which are arranged in the plating bath (2).12. An apparatus according to claim 10, wherein the supports (10) areadjustable.
 13. An apparatus according to claim 10, wherein the supports(10) are at least one of height-adjustable and adjustable sideways. 14.An apparatus according to claim 10, wherein there are envisaged contactelements (13) for electrically contacting the semiconductor component(1), which are each arranged in an extension of one of the supports (10)outside the plating bath (2).
 15. A method for producing a semiconductorcomponent (1) comprising the following steps: Providing a plating bath(2) with an electrolyte (3), a first electrode (4) arranged in theplating bath (2) and a second electrode (5) arranged outside the platingbath (2), providing an irradiation device (15) for generatingelectromagnetic radiation, providing a semiconductor substrate (6) of aplanar design with a first side (7) and a second side (8) lying oppositethereto, immersing at least the second side (8) of the semiconductorsubstrate (6) into the electrolyte (3), producing an electrical contactbetween the first side (7) of the semiconductor substrate (6) and thesecond electrode (5), irradiating at least the first side (7) of thesemiconductor substrate (6) by means of the irradiation device (15). 16.A method according to claim 15, wherein the semiconductor substrate (6)is immersed on partly into the electrolyte (3).
 17. A method accordingto claim 15, wherein the semiconductor substrate (6) is immersed on intothe electrolyte (3) only so far that the first side (7) remains dry. 18.A method according to claim 15, wherein the semiconductor substrate (6),after immersion into electrolyte (3), is lifted back out of theelectrolyte so far that a surface meniscus (17) forms between the secondside (8) of the semiconductor substrate (6) and the electrolyte (3). 19.A method according to claim 15, wherein the semiconductor substrate (6)is immersed fully into the electrolyte (3), however, only so far thatthe first side (7) is covered by a layer of a depth of a maximum 10 mm.20. A method according to claim 15, wherein the semiconductor substrate(6) is immersed fully into the electrolyte (3), however, only so farthat the first side (7) is covered by a layer of a depth of a maximum 5mm.
 21. A method according to claim 15, wherein the semiconductorsubstrate (6) is immersed fully into the electrolyte (3), however, onlyso far that the first side (7) is covered by a layer of a depth of amaximum 2 mm.
 22. A method according to claim 15, wherein the first side(7) of the semiconductor substrate (6) is its rear side.
 23. A methodaccording to claim 15, wherein the first side (7) of the semiconductorsubstrate (6) is its front side.
 24. A semiconductor component (1)comprising a. a semiconductor substrate (6) with i. a first side (7),ii. a second side (8) lying opposite thereto and iii. a thickness (D) ina direction vertically to the sides (7, 8), b. with at least the firstside (7) being designed such that it is, at least in some areas, atleast 50% permeable for the electromagnetic radiation with a wavelengthin the range of 650 nm to 1200 nm.
 25. A semiconductor component (1)according to claim 24, wherein the semiconductor substrate (6) isdesigned such that it is at least 50% permeable, at least in some areas,in at least one direction for electro-magnetic radiation with awavelength in the range of 650 nm to 1200 nm up to a penetration depthof at least 50% of the thickness (D).
 26. A semiconductor component (1)according to claim 24, wherein the semiconductor substrate (6) isdesigned such that it is at least 50% permeable, at least in some areas,in at least one direction for electromagnetic radiation with awavelength in the range of 650 nm to 1200 nm up to a penetration depthof at least 75% of the thickness (D).
 27. A semiconductor component (1)according to claim 24, wherein the semiconductor substrate (6) isdesigned such that it is at least 50% permeable, at least in some areas,in at least one direction for electromagnetic radiation with awavelength in the range of 650 nm to 1200 nm up to a penetration depthof at least 90% of the thickness (D).